Systems and methods for drive circuits for dynamic magnetic stripe communications devices

ABSTRACT

Dynamic magnetic stripe communications devices are provided as magnetic stripe emulators. A magnetic stripe emulator may include a coil. Drive circuits may be coupled to this coil in order to produce electromagnetic fields from the coil operable to communicate with a magnetic stripe reader.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/305,021, titled “SYSTEMS AND METHODS FOR DRIVECIRCUITS FOR DYNAMIC MAGNETIC STRIPE COMMUNICATIONS DEVICES,” filed Feb.16, 2010 (Attorney Docket No. D/032 PROV), which is hereby incorporatedby reference herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to magnetic cards and devices and associatedpayment systems.

SUMMARY OF THE INVENTION

A card may include a dynamic magnetic communications device. Such adynamic magnetic communications device may take the form of a magneticencoder or a magnetic emulator. A magnetic encoder may change theinformation located on a magnetic medium such that a magnetic stripereader may read changed magnetic information from the magnetic medium. Amagnetic emulator may generate electromagnetic fields that directlycommunicate data to a magnetic stripe reader. Such a magnetic emulatormay communicate data serially to a read-head of the magnetic stripereader.

All, or substantially all, of the front as well as the back of a cardmay be a display (e.g., bi-stable, non bi-stable, LCD, LED, orelectrochromic display). Electrodes of a display may be coupled to oneor more capacitive touch sensors such that a display may be provided asa touch-screen display. Any type of touch-screen display may beutilized. Such touch-screen displays may be operable of determiningmultiple points of touch. Accordingly, a barcode may be displayed acrossall, or substantially all, of a surface of a card. In doing so, computervision equipment such as barcode readers may be less susceptible toerrors in reading a displayed barcode.

A card may include a number of output devices to output dynamicinformation. For example, a card may include one or more RFIDs or ICchips to communicate to one or more RFID readers or IC chip readers,respectively. A card may include devices to receive information. Forexample, an RFID and IC chip may both receive information andcommunicate information to an RFID and IC chip reader, respectively. Adevice for receiving wireless information signals may be provided. Alight sensing device or sound sensing device may be utilized to receiveinformation wirelessly. A card may include a central processor thatcommunicates data through one or more output devices simultaneously(e.g., an RFID, IC chip, and a dynamic magnetic stripe communicationsdevice). The central processor may receive information from one or moreinput devices simultaneously (e.g., an RFID, IC chip, dynamic magneticstripe devices, light sensing device, and a sound sensing device). Aprocessor may be coupled to surface contacts such that the processor mayperform the processing capabilities of, for example, an EMV chip. Theprocessor may be laminated over and not exposed such that such aprocessor is not exposed on the surface of the card.

A card may be provided with a button in which the activation of thebutton causes a code to be communicated through a dynamic magneticstripe communications device (e.g., the subsequent time a read-headdetector on the card detects a read-head). The code may be indicativeof, for example, a merchant code or incentive code. The code may bereceived by the card via manual input (e.g., onto buttons of the card)or via a wireless transmission (e.g., via light, electromagneticcommunications, sound, or other wireless signals). A code may becommunicated from a webpage (e.g., via light and/or sound). A card mayinclude a display such that a received code may be visually displayed toa user. In doing so, the user may be provided with a way to select, anduse, the code.

A dynamic magnetic stripe communications device may include a magneticemulator that comprises an inductor (e.g., a coil). Current may beprovided through this coil to create an electromagnetic field operableto communicate with the read-head of a magnetic stripe reader. The drivecircuit may fluctuate the amount of current travelling through the coilsuch that a track of magnetic stripe data may be communicated to aread-head of a magnetic stripe reader. A switch (e.g., a transistor) maybe provided to enable or disable the flow of current according to, forexample, a frequency/double-frequency (F2F) encoding algorithm. In doingso, bits of data may be communicated.

A closed loop linear analog drive circuit may be provided to preciselydefine the current flow at any and all points in time. In doing so, theclosed loop linear analog drive circuit may create any desiredelectromagnetic field at any time. Accordingly, the accuracy andreliability of a magnetic emulator may be enhanced.

Each track of magnetic stripe information may utilize, for example, aseparate instance of a drive circuit coupled to a separate magneticemulator having a coil. Enabling circuitry may be coupled to one or moredrive circuits and/or magnetic emulators to enable the use of suchcomponents.

An input signal may be provided from, for example, a microprocessor orother circuitry. Several microprocessors may, for example, be includedon a card or other device (e.g., a mobile telephonic device). A rampgenerator may be provided, for example, to convert a positive ornegative going level transition of an input signal into either apositive going or negative going linear ramp of defined slope. Thissignal of, for example, alternative positive and negative ramps may bepassed to additional signal processing circuitry.

Signal shaping circuitry may be provided and may, for example, receivethe signal provided by the ramp generator. The signal shaping circuitrymay be utilized to shape the ramp signals provided by the rampgenerator.

The shaped signals may be provided to current control circuitry. Thecurrent control circuit may be utilized, for example, to control thelevel of current at an output node.

A control input may be provided, for example, that provides a mutingfunction. When such a control signal is pulled high to the supplyvoltage, for example, the drive current may be forced to approximately 0A (e.g., 0 A). Such a muting function may be utilized, for example, tosilence a dynamic magnetic stripe communications device during power-upand power-down of the drive circuits. When such circuits are not in use,for example, power may be removed to increase battery life. During apower transition, for example, the mute function may prevent unwantedsignals (e.g., pulses) from being generated.

A reference voltage may be utilized by a voltage regulator. In doing so,for example, the dependence on a supply voltage may be eliminated. Forexample, a battery may be supercharged and this battery may havedifferent voltage levels during the battery's use. A reference voltageprovided from a voltage regulator may, for example, provide a morereliable source of electrical energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The principles and advantages of the present invention can be moreclearly understood from the following detailed description considered inconjunction with the following drawings, in which the same referencenumerals denote the same structural elements throughout, and in which:

FIG. 1 is an illustration of cards constructed in accordance with theprinciples of the present invention;

FIG. 2 is an illustration of a process flowchart and waveformsconstructed in accordance with the principles of the present invention;

FIG. 3 is an illustration of an architecture constructed in accordancewith the principles of the present invention;

FIG. 4 is a schematic of a circuit constructed in accordance with theprinciples of the present invention;

FIG. 5 is a schematic of a circuit constructed in accordance with theprinciples of the present invention; and

FIG. 6 is an illustration of a process flow chart constructed inaccordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows card 100 that may include, for example, a dynamic numberthat may be entirely, or partially, displayed via display 112. A dynamicnumber may include a permanent portion such as, for example, permanentportion 111. Permanent portion 111 may be printed as well as embossed orlaser etched on card 100. Multiple displays may be provided on a card.For example, display 113 may be utilized to display a dynamic code suchas a dynamic security code. Display 125 may also be provided to displaylogos, barcodes, as well as multiple lines of information. A display maybe a bi-stable display or non bi-stable display. Permanent information120 may also be included and may include information such as informationspecific to a user (e.g., a user's name or username) or informationspecific to a card (e.g., a card issue date and/or a card expirationdate). Card 100 may include one or more buttons such as buttons 130-134.Such buttons may be mechanical buttons, capacitive buttons, or acombination or mechanical and capacitive buttons. Card 100 may includebutton 199. Button 199 may be used, for example, to communicateinformation through dynamic magnetic stripe communications device 101indicative of a user's desire to communicate a single track of magneticstripe information. Persons skilled in the art will appreciate thatpressing a button (e.g., button 199) may cause information to becommunicated through device 101 when an associated read-head detectordetects the presence of a read-head of a magnetic stripe reader. Button198 may be utilized to communicate (e.g., after button 198 is pressedand after a read-head detects a read-head of a reader) informationindicative of a user selection (e.g., to communicate two tracks ofmagnetic stripe data). Multiple buttons may be provided on a card andeach button may be associated with a different user selection.

Architecture 150 may be utilized with any card. Architecture 150 mayinclude processor 120. Processor 120 may have on-board memory forstoring information (e.g., drive code). Any number of components maycommunicate to processor 120 and/or receive communications fromprocessor 120. For example, one or more displays (e.g., display 140) maybe coupled to processor 120. Persons skilled in the art will appreciatethat components may be placed between particular components andprocessor 120. For example, a display driver circuit may be coupledbetween display 140 and processor 120. Memory 142 may be coupled toprocessor 120. Memory 142 may include data that is unique to aparticular card. For example, memory 142 may store discretionary datacodes associated with buttons of card 150. Such codes may be recognizedby remote servers to effect particular actions. For example, a code maybe stored on memory 142 that causes a promotion to be implemented by aremote server (e.g., a remote server coupled to a card issuer'swebsite). Memory 142 may store types of promotions that a user may havedownloaded to the device and selected on the device for use. Eachpromotion may be associated with a button. Or, for example, a user mayscroll through a list of promotions on a display on the front of thecard (e.g., using buttons to scroll through the list).

Any number of reader communication devices may be included inarchitecture 150. For example, IC chip 152 may be included tocommunicate information to an IC chip reader. IC chip 152 may be, forexample, an EMV chip. As per another example, RFID 151 may be includedto communicate information to an RFID reader. A magnetic stripecommunications device may also be included to communicate information toa magnetic stripe reader. Such a magnetic stripe communications devicemay provide electromagnetic signals to a magnetic stripe reader.Different electromagnetic signals may be communicated to a magneticstripe reader to provide different tracks of data. For example,electromagnetic field generators 170, 180, and 185 may be included tocommunicate separate tracks of information to a magnetic stripe reader.Such electromagnetic field generators may include a coil wrapped aroundone or more materials (e.g., a soft-magnetic material and a non-magneticmaterial). Each electromagnetic field generator may communicateinformation serially to a receiver of a magnetic stripe reader for aparticular magnetic stripe track. Read-head detectors 171 and 172 may beutilized to sense the presence of a magnetic stripe reader (e.g., aread-head housing of a magnetic stripe reader). This sensed informationmay be communicated to processor 120 to cause processor 120 tocommunicate information serially from electromagnetic generators 170,180, and 185 to magnetic stripe track receivers in a read-head housingof a magnetic stripe reader. Accordingly, a magnetic stripecommunications device may change the information communicated to amagnetic stripe reader at any time. Processor 120 may, for example,communicate user-specific and card-specific information through RFID151, IC chip 152, and electromagnetic generators 170, 180, and 185 tocard readers coupled to remote information processing servers (e.g.,purchase authorization servers). Driving circuitry 141 may be utilizedby processor 120, for example, to control electromagnetic generators170, 180, and 185.

FIG. 2 shows process 201 that may include, for example, ramp generator202, signal shaping 203, and current control 204. A control signal maybe generated by, for example, a microprocessor or other controlcircuitry. Such a control signal may be utilized by ramp generator 202to, for example, generate a linear increasing or a linear decreasingsignal. The slope of the signal may be pre-determined and stored inmemory. The slope of the signal may be changed. For example, the slopeof the signal may be different depending on, for example, theenvironment that is sensed by a card or other device (e.g., adetermination by a read-head detector that a particular type of readeris being utilized). The signal produced by ramp generator 202 may alsobe controlled to produce frequency/double-frequency (F2F) encodedinformation by the microprocessor. Such information may be shaped by,for example, signal shaping 203. Signal shaping 203 may be utilized toshape the signal produced by ramp generator 202 to provide, for example,a non-linear shape in the signal. Current control circuitry 204 may beutilized, for example, to control the current of the output signal fromprocess 201.

Signal 210 may be provided, for example, from a ramp generator providinga ramp generator signal. The ramp generator may receive, for example, acontrol signal on when ramp generator should produce an increasingsignal, decrease the signal, or leave the output signal steady. Theincreasing signal may be limited, for example, at a voltage threshold inthe positive or negative directions. The decreasing signal may belimited, for example, at a voltage threshold in the positive or negativedirections. For example, the ramp may occur in a single polarity oracross both the positive and negative polarities.

Signal 215 may be provided, for example, to provide a ramped signal inthe positive polarity. The maximum threshold may be, for example,between approximately 2.2 and 3.6 volts (e.g., approximately 2.7 volts).The minimum threshold may be, for example, between approximately 0 and0.1 volts (e.g., 0 volts). Person skilled in the art will appreciatethat the ramp generator may hold a peak for a particular amount of time.For example, the ramp generator may hold a peak at an amount of timegreater than it took the predecessor (or successor) ramp to be providedfrom the ramp generator. In doing so, for example, a cleaner signal maybe provided to a read-head of a magnetic stripe reader. Alternatively,for example, the ramp generator may hold a peak at an amount of timeless than, or equal to, the time it took the predecessor (or successor)ramp to be provided from the ramp generator. Signal 215 may, forexample, be provided as a trapezoidal wave signal.

Signal 220 may be, for example, the shaped signal provided to a currentcontrol circuit (e.g., from a signal shaping circuit). The shaped signalmay provide, for example, shaped trapezoidal segments (e.g., segment221) to a current control circuit. A current may then be provided, forexample, to a coil of a magnetic emulator from the current controlcircuitry that is a function, for example, of the voltage provided fromthe signal shaping circuit. Signal 220 may include, for example,sinusoidal and arctangent signal characteristics beyond thecharacteristics present in the ramped signal from the ramp generator.More particularly, the shaped signal may smooth and curve the transitionpoints in the ramped signal (e.g., point 219 of signal 215). In doingso, a signal with less noise and ringing may, for example, be providedto a read-head of a magnetic stripe reader. Persons skilled in the artwill appreciate that constant voltage portions of a ramp signal (e.g.,portion 217 of signal 215) may also provide areas of constant voltage inshaped signal. The areas of constant voltages between a ramp generatedsignal and a shaped signal, however, may differ in length (e.g., thelength of constant voltages in a shaped signal may be shorter).

Signal 225 may be, for example, the change in current with respect tochange in time signal received by a read-head of a magnetic stripereader as a result of receiving a signal from a coil driven by thecurrent signal produced by control circuit 204. Persons skilled in theart will appreciate increases in voltages in signal 220 may result inpositive pulses (e.g. pulse 226) of signal 225 and decreases in voltagesin signal 220 may result in negative pulses (e.g., pulse 227) in signal225.

FIG. 3 shows processor 310 that provides drive (e.g., signal 311) andmute signals (e.g., signal 312) to drive circuitry (e.g., drivecircuitry 320) as well as control signals (e.g., signal 319) to enablingcircuitry 360. Drive circuitry may provide dynamic magneticcommunications device drive signals (e.g., signal 321) to dynamicmagnetic communications devices (e.g., device 370). A different drivecircuit may be utilized, for example, for a different dynamic magneticcommunications device (e.g., a different emulator, having a coil, forcommunicating a different track of magnetic stripe data). A differentprocessor may provide, for example, drive and mute signals to suchdifferent drive circuit.

A drive circuit may include, for example, a ramp generator circuit(e.g., ramp generator 202 of FIG. 2), signal shaping circuit (e.g.,signal shaping circuit 203 of FIG. 3), and current control circuit(e.g., current control circuit 204 of FIG. 2). Drive circuitry (e.g.,drive circuitry 320) may provide a shaped signal to a dynamic magneticstripe communications device (e.g., device 370). Similarly, for example,enabling circuitry 360 may provide enabling signals (e.g., signals 361)to, for example, drive circuitry and dynamic magnetic stripecommunication devices.

A single processor may be utilized, for example, to control one, two,three, or four drive circuits and magnetic emulators for communicationof separate tracks of magnetic stripe data. A single enabling circuitmay be utilized to enable, for example, one, two, three, or fourmagnetic emulators. For example, a single enabling circuit may beutilized to enable two magnetic emulators while a single processor maybe utilized to provide control and mute signals to drive two circuits(e.g., one for each emulator). Alternatively, more than one processormay be utilized, for example, to control separate drive circuits andmore than one enabling circuit may be utilized to enable separatemagnetic emulators.

FIG. 4 may include circuitry 400 that may include, for example, firstsource voltage 401, second source voltage 402, ground 499, drive signal412, mute signal 411, output signal 413, transistors 441-445, capacitors451 and 452, resistors 421-431, diodes 471-473, and operationalamplifiers 461 and 462. Persons skilled in the art will appreciate thatcircuitry 400 may be utilized as a drive circuit for communicating atrack of magnetic stripe data through a magnetic emulator. A magneticemulator may include, for example, an inductor such as a coil. Such acoil may be fabricated, for example, on a flexible, printed circuitboard such as a multiple-layer flexible, printed circuit board.

Capacitor 451 may have approximately, for example, between 1800 and 3500pF (e.g., approximately 2200 pF). Capacitor 451 may be utilized, forexample, to control the width of pulses in a signal received by aread-head of a magnetic stripe reader (e.g., the width of pulse 226 ofsignal 225 of FIG. 2).

Drive signal 412 may be provided, for example, from a processor. A rampgenerator circuit may be provided that may include, for example,resistors 421 and 422, transistors 441-444, capacitor 451, andoperational amplifier 461.

The ramp generator circuit may include operational amplifier 461, whichmay serve as an impedance buffer for the output of the ramp generatorcircuit. Accordingly, for example, the voltage across capacitor 451 maynot be loaded by subsequent circuitry. Transistors 443 and 444 may, forexample, be coupled to form a temperature compensated constant currentsource. The current level may be defined, for example, by resistor 422.The input signal (e.g., drive signal 412) may be, for example, eithergrounded (e.g., at zero voltage equal to ground 499) or left floating(e.g., open collector active pull-down driven). The resulting constantcurrent may be, for example, selectively applied to capacitor 451, whosevoltage may then be linearly increased when desired to form a positivegoing ramp reaching, but not exceeding, for example, supply voltage 401.

A microprocessor may be configured to provide the characteristics of aramp generator, shaping signal circuit, as well as a current controlcircuit. Alternatively, for example, such ramp generator, shapingsignal, and current control circuits may be provided on an ASIC ormultiple ASICs. Multiple drive circuits may be provided on an ASIC. Forexample, a single ASIC may provide two or three drive circuits which, inturn, may be utilized to cause two or three, respectively, dynamicmagnetic communications devices (e.g., magnetic emulators) tocommunicate different tracks of data to a read-head of a magnetic stripereader.

Transistors 441 and 442 may be coupled, for example, to form atemperature compensated constant current sink with a current leveldefined by resistor 421. The circuit comprising transistors 441 and 442may, for example, consistently draw a constant current which, in turn,may deplete the charge on capacitor 451 when the current source fromtransistors 443 and 444 is inoperative and deducts from the sourcedcurrent when the current source from transistors 443 and 444 isoperative.

The current source created by transistors 443 and 444, for example, maydeliver approximately twice the current utilized by the current sinkcreated by 441 and 442. This may be achieved, for example, by settingresistor 421 to approximately twice the value of resistor 422. As aresult, for example, the state of input 412 may define whether capacitor451 is charged or depleted by matched current values of opposing sign.The result, for example, may be an output of positive going or negativegoing linear ramps of equal, but opposite sign slope.

A signal shaping functionality may be applied to, for example, thesignal produced by the ramp generator circuit. Accordingly, for example,a signal shaping circuit may be provided and may include, for example,resistors 423-428 and diodes 471-472. The ramp signal from the rampcircuit may be provided to, for example, resistor 423. The resultingshaped signal from the shaping circuit may be provided, for example, atthe common point between resistors 424 and 428.

The signal shaping circuit may include diodes 471 and 472. The signalshaping circuit may include additional diodes. Such diodes may be biasedto impart their linear characteristics onto the signal being received bythe shaping circuit. Resistors 423-426 and 428 may be bias resistorsthat are selected to provide a smooth transition from, for example, thezero volt level through to the reference voltage 401 beginning with aslope of approximately zero volts/second and finishing with a slope ofapproximately zero volts/second. The resultant shape may be similar to,for example, approximately an arctangent curve. The resistor pair 424and 438 may present, for example, a portion of the resulting shapedsignal to the positive terminal of operational amplifier 462.

A current control functionality may be applied to, for example, thesignal produced by the signal shaping circuit. Accordingly, for example,a current control circuit may be provided and may include, for example,resistors 429-431, operational amplifier 462, transistor 445, capacitor452 and diode 473. The shaped signal from the signal shaping circuit maybe provided to, for example, the positive terminal of operationalamplifier 462, which is operable to control the level of current atoutput 413. The current from output 413 may, for example, be passedthrough a magnetic emulator (e.g., through a coil) connected betweenoutput 413 and a positive supply voltage (e.g., supply voltage 402). Thecoil may be utilized to serial transmit a track of magnetic stripe data.

Operational amplifier 462 and feedback resistor 430 may control, forexample, the collector-base current of transistor 445 so as to establisha voltage across sense resistor 431 related to the incoming signal. Inthis manner, the current drawn through a coil of a magnetic emulator,for example, may be precisely controlled.

Resistor 429 may, for example, provide an offset such that the drivencurrent corresponding to the zero volt level of the signal input comesclose to approximately, but does not reach, zero milliamps. For example,the current may be, for example, limited to approximately 2-3 milliamps(e.g., approximately 2 milliamps). Accordingly, transistor 445 mayremain active and not shut-off, thereby avoiding, for example,non-linear and abrupt changes in current that are undesirable in thefinal output signal.

Resistor 431 may be, for example, a sense resistor. Resistor 431 may beselected, for example, so as to scale the current to levels needed tooperate a dynamic magnetic stripe communications device. The currentassociated with the maximum input signal (e.g., at reference voltage401) may have, for example, a range between 50-100 milliamps.Alternatively, for example, the current may be above or below thisrange.

A dynamic magnetic stripe communications device may, for example, beprovided between output 413 and supply voltage 402. A high pass filtermay be provided. Such a high pass filter may include, for example acapacitor such as capacitor 452. Such a high pass filter may, forexample, prevent abrupt signal changes that include high frequencycomponents from reaching the dynamic magnetic stripe communicationsdevice.

Diode 473 may be provided. Diode 473 may provide back-EMF protection forthe drive circuitry when, for example, the output drives an inductiveload.

An auxiliary control signal may be provided, for example, to provide amute functionality. Such a mute signal (e.g., signal 411) may beutilized to force the drive current, for example, to zero amperes (e.g.,if pulled up). The signal, for example, may be left floating as neededduring normal feedback control. The muting functionality may beutilized, for example, to silence a dynamic magnetic stripecommunications device during power-up and power-down of the drivecircuits. When not in use, for example, the power may be removed fromthese circuits to increase battery life. During a power transition,however, undesirable signals/pulses may be generated. The mutingfunctionality may be utilized to prevent such undesirablesignals/pulses.

A sequence may include, for example, holding the mute signal high,applying power to the drive circuits, releasing the mute signal, drivingdata to the dynamic magnetic stripe communications device, pulling themute signal high, removing power from the drive circuits, and settingcircuitry for optimum low-power stand-by operation.

Persons skilled in the art will appreciate that low-power operation maybe optimized. FIG. 5 shows power control circuit 500 that may include,for example, enable circuitry 511, resistor 531, switching component521, component 561, capacitors 551-563, source voltages 501, 502, and503, and ground 599.

Switching component 521 may be, for example, a MOSFET. Switchingcomponent 521 may be used to, for example, switch current and thereforepower from a power supply that may be a battery (e.g., power source501). A MOSFET may be utilized as a switching component, for example,that has a low series resistance in an ON mode. A control signal (e.g.,signal 511), which may be supplied by a microprocessor or other circuit,may be utilized to turn ON or OFF switching component 521.

Persons skilled in the art will appreciate that power usage may beminimized by, for example, providing control signal 511 in ahigh-impedance state (floating) when switching device 521 is to be inthe OFF state. For this reason, for example, resistor 531 is provided tohold switching device 521 in the OFF state.

The output of switching device 521 may, for example, supply the VCCpower to the output stages of the current control circuit of circuit 400of FIG. 4 as well as, for example, the operational amplifiers of circuit400 of FIG. 4. Additionally, for example, power may be supplied toadditional circuits utilizing reference voltages.

A reference voltage (e.g., voltage 401 of FIG. 4 and voltage 503 of FIG.5) may be provided, for example, by a voltage regulator (e.g., component561 of FIG. 5). A reference voltage may, for example, remove thedependence on a supply voltage (e.g., voltage 402 of FIG. 4). The supplyvoltage may vary in cases where, for example, a battery is utilized asthe overall power source and the battery may discharge through use.

A low drop-out (LDO) linear regulator may be utilized as a voltageregulator. Zener diode circuits may also be utilized. A resultingvoltage reference may be filtered by, for example, capacitor 563 orother circuits. The voltage reference may be provided, for example, at apoint below the minimum possible supply voltage. Accordingly, a batterymay be provided and discharged to approximately 2.8 volts. Accordingly,a reference voltage may be provided at approximately 2.7 volts.Accordingly, the difference between a supply voltage and referencevoltage may be between 0.2 volts and 0.5 volts (e.g., approximately 0.1volts).

A signal shaper circuit may, for example, utilize any number of diodes(e.g., approximately 9 diodes) and bias resistors to provide a moreprecise implementation of an arctangent waveform. Additional diodes mayintroduce, for example, additional breakpoints in a piecewiseapproximation of the desired waveform. Resistors 425, 427, and 426 may,for example, be replaced with two adjustable voltage references, whichmay be different from voltage 401 (e.g., half of voltage of voltage 401and/or may differ from voltage 401 by approximately 0.5−1.5 or 1 volts).

The current drive may be, for example, provided by replacing theoperational amplifier with one or more individual transistors in an openloop control configuration. Persons skilled in the art will appreciatethat transistors may be, for example, replaced with MOSFETs (e.g., incircuit 400 of FIG. 4). The operational amplifier in a ramp generatorcircuit may, for example, be replaced with a pair of transistors in apush-pull arrangement.

FIG. 6 shows a sequence to communicate magnetic stripe data to amagnetic stripe reader. The sequence may include, for example, holdingthe mute signal high (e.g., step 601 of FIG. 6), applying power to thedrive circuits (e.g., step 602 of FIG. 6), releasing the mute signal(e.g., step 603 of FIG. 6), driving data to the dynamic magnetic stripecommunications device (e.g., step 604 of FIG. 6), pulling the mutesignal high (e.g., step 605 of FIG. 6), removing power from the drivecircuits, and setting circuitry for optimum low-power stand-byoperation. All or a portion of the process may be repeated multipletimes such that a card may be swiped multiple times at a magnetic stripereader. Read-head detectors may be provided on a card to determine if,for example, a card is being re-swiped at a magnetic stripe reader.Low-power stand-by operation may include, for example, placing amicroprocessor in a sleep mode. A microprocessor may be awakened fromsleep mode, for example, by a card (or other device) receiving manualinput from a user. For example, a user may press a button on a card toselect a feature, the microprocessor may be awakened from sleep mode,and magnetic stripe data may be communicated by a drive circuit anddynamic magnetic stripe communications device to a magnetic stripereader when circuitry on the card determines that dynamic magneticstripe communications device is within the proximity of a read-head of amagnetic stripe reader to communicate magnetic stripe data (e.g., viaone or more magnetic stripe read-head detectors provided on the card orother device).

Persons skilled in the art will appreciate that a boost circuit may beprovided. A battery (e.g., a battery having approximately 3.6 volts fornormal operation) may be supercharged to a higher voltage (e.g.,approximately 3.8 to 4.5 volts such as approximately 4.2 volts). Themicroprocessor, however, may not be able to directly utilize the voltagefrom a supercharged battery. As a result, for example, a boost circuitmay be provided to step down the voltage of a supercharged battery to alevel that may be utilized by a microprocessor. The boost circuitry maydetermine when the battery discharges past a particular threshold (e.g.,to a voltage suitable to directly power a microprocessor) so that theboost circuitry may stop stepping down the voltage of the battery. Theboost circuitry may also change the voltage the battery is stepped down.Accordingly, for example, as the voltage supplied by a batterydecreases, the boost circuitry may decrease the amount of voltage thebattery is stepped down. In doing so, additional power may be obtainedfrom a battery without, for example, damaging the microprocessor orcausing the microprocessor to malfunction.

Persons skilled in the art will also appreciate that the presentinvention is not limited to only the embodiments described. Instead, thepresent invention more generally involves dynamic information. Personsskilled in the art will also appreciate that the apparatus of thepresent invention may be implemented in other ways then those describedherein. All such modifications are within the scope of the presentinvention, which is limited only by the claims that follow.

1-17. (canceled)
 18. A power control circuit, comprising: a switchingdevice with low ON mode series resistance operable to switch a powersupply signal from a power source to a drive circuit in response to anon-high impedance state of a control signal; a circuit componentconfigured to hold the switching device in an OFF state in response to ahigh-impedance state of the control signal; and a voltage regulatorconfigured to provide at least one reference signal to the drivecircuit.
 19. The device of claim 18, further comprising a filterconfigured to filter the at least one reference signal.
 20. The deviceof claim 18, further comprising a capacitor configured to filter thereference signal.
 21. The device of claim 18, wherein the voltageregulator is a low drop-out linear regulator.
 22. The device of claim18, wherein the voltage regulator is a zener diode circuit.
 23. Thedevice of claim 18, wherein a magnitude of the at least one referencesignal below a minimum magnitude of the supply signal.
 24. The device ofclaim 18, wherein the switching device is a metal oxide semiconductorfield effect transistor.
 25. The device of claim 18, wherein the controlsignal is a control signal of a processor.
 26. The device of claim 18,wherein the power supply signal is a current provided by a battery. 27.The device of claim 18, wherein the switching device is operable toprovide an output signal to at least one output stage of a currentcontrol circuit of the drive circuit.
 28. The device of claim 18,wherein the drive circuit includes a plurality of operationalamplifiers, and the switching device is operable to provide an outputsignal to at least one output stage of a current control circuit of thedrive circuit and to the plurality of operational amplifiers.
 29. Thedevice of claim 18, wherein the voltage regulator is configured toprovide the reference signal independent of a magnitude of the powersupply signal.
 30. The device of claim 18, wherein the power supplysignal is received by the voltage regulator from a battery, the powersupply signal varies based on a charge of the battery, and the voltageregulator is configured to provide the reference signal independent of amagnitude of the power supply signal.
 31. The device of claim 18,wherein the reference signal is a plurality of reference signals, thepower supply is a battery; the plurality of reference signals are afirst voltage and a second voltage, and a magnitude of each of the firstvoltage and second voltage is selected from the group consisting of(0.5)*(the battery voltage less 0.2 v-0.5 v) and the battery voltageless 0.7 v-2 v.
 32. The device of claim 18, wherein the drive circuitincludes an operational amplifier and one or more transistors of a rampgenerator in an open loop control configuration, and the switchingdevice is operable to provide an output signal to the operationalamplifier, at least one output stage of a current control circuit, andthe one or more transistors.